Elevator system



J. H. BORDEN Sept. 4, 1934.

ELEVATOR SYSTEM Filed Sept. 15, 1933 INVENTOR.

M QQ 0/ W A TTORNEY.

Patented Sept. 4, 1934 UNITED sTATEs 1.972.312 V ELEVATOR srs'rmr Joseph H.

Borden, Elkins Park, Pa.,

asslgnor to Atlantic Elevator Company, Philadelphia, Pa, a corporation of Pennsylvania Application September 15, 1933, Serial No. 689,605 9 Claims. (cl. 173-152) 4 My invention relates to high speed elevator systems and the like having variablevoltage or Ward-Leonard type of speed control.

In accordance with my invention, rapid and accurate levelling is obtained by maintaining the flow of current in the generator field always in one direction and effecting levelling by reversal of the connections between the car-driving motor and its supply generator. 1

My invention further resides in the features hereinafter'described and claimed.

For an understanding of my invention, and

for illustration of a preferred form thereof, reference is to be hadto the accompanying drawing which diagrammatically illustrates an elevator system embodying it.

Heretofore, in systems using vvariable voltage, or Ward-Leonard type of control, low speed for levelling was obtained by reducing the field excitation of the generator supplying the car motor to low value, and reversing the field excitation to another low value to correct for overshooting beyond the desired landing. Suitable magnitude of'low speedis more or less fixed by the accuracy of the landings desired and is, for example, of the order of 30 feet per minute.

With low speed elevator systems, this method of levelling was fairly satisfactory. However, with the advent of high-speed systems in which the running speed may be as high as 1200 feet per minute, the levelling speed remaining -necessarily about the same for accurate landings, this method of levelling is not practical. Even with systems of moderately high speed, as 300 ft. per minute, the car after over-shooting the desired landing would often hesitate for an appreciable length of time before travelling back to the desired level and, in some cases, after hesitating, would resume movement in the direction away from the desired landing before eventually reversing its direction. for proper levelling.

A levelling operation of the car, in general, consists, after running in one direction, of travelling at a materially lower speed in the same direction and then reversal of movement at low speed. However, with the aforesaid control, the voltages generated and applied to the car motor at these two low speeds, in opposite direction, are not the same and in most cases are materially different. The discrepancy is due principally to hysteresis of the iron of the generator field and' partly due to the inductances of the windings. As the residual magnetism of the field is determined by the strength of the prior energizing current, it is clear that the voltage generated when the field is feebly excited in a reverse direction may even be of the same polarity as be- "fore, or if the field current is enough to overcome the residual, the generated voltage though of the proper polarity may still be unduly small, at least initially, and require appreciable time to build up to its desired value. As the running speed of the system is increased, the eiiect of the hysteresis 'of the iron more and more adversely affects the levelling operation. This is because of the fact that ina Ward-Leonard control system with constant motor field the generator voltage is roughly proportional to the speed. In the higher speed systems the generator voltage corresponding to levellingspeed which, as stated above, is fixed by the landing accuracy required and is thus independent of the maximum operating speed of the system, becomes a smaller and smaller fraction of the maximum generator voltage corresponding with full speed operation. Taking the figures of the example given above, for example, with a maximum speed of 1200 feet per minute and a levelling speed of 30 feet per minute, the levelling voltage is 1/40 of the maximum voltage, which may be of the same order of magnitude as the voltage due to the residual fleld of the generator, in some instances being even less.

When the car is travelling at full speed, slowing down to levelling speed in the same direction, corresponding to a given setting of the generator field resistance, the voltage-generated by the residual field acts cumulatively with the field excitation. In case the car overshoots the landing, the same field excitation is applied in an opposite sense and the voltage due to the residual field acts diiferentially with respect to the field excitation, that is, the difference in the generated voltage-in levelling in the same direction as previous travel and that levelling in the opposite direction is equal to twice the voltage due to the residual field. If the residual voltage is a substantial component of, or the same order of magnitude of, the total voltage in the levelling setting of the generator field resistance, the levelling-up speed and the levelling-down speed will be widely diiferent. In extreme cases the residual voltage may be greater than that due to the field excitation in the levelling setting of the generator field rheostat so that there is no reversal of the levelling voltage and it is impossible to level the elevator in the ordinary manner.

To give a specific example made one system of only moderate speed, it is found that immediately after running full speed up, the levellingup voltage was about 15 volts; whereas, when the field reversed for levelling down, the voltage was 9 volts or less, increasing to only about 10 volts after an interval of six seconds. Immediately after running full speed down, the levelling-up voltage was 1!) volts, increasing to about 11 volts in six seconds, and in re-levelling down, the voltage was about 14% volts. That is, after operating full speed up, the residual voltage is one-half of the diiference between 15V; volts and 9 volts or 3 /4 volts, which is more than one-third of the levelling-down voltage. After full speed down operation, the residual voltage equals 2% volts or nearly one-fourth of the levelling up voltage. In each case the levelling speed in one direction is approximately 50 per cent. greater than in the other direction. These conditions are far from extremes often encountered in actual installations, and the diiferences are greatly accentuated in high-speed systems. It is apparent that with such differences in the magnitude of the generator voltage at low speed, there is an appreciable time lag before the car is finally brought to the floor level.

It has become almost the universal practice for moderate speed installations substantially to increase the size of the electrical equipment in order that the required torque for levelling may be obtained, even at the reduced voltages obtainable at low levelling speeds. This expedient, however, is impractical and economically unfeasible for modern high-speed systems.

In accordance with my invention, recognizing that the difliculties of levelling are principally due to the reversal of direction of the field flux in the driving generator, in my system the field flux is maintained always in the same. direction, and the reversal of the main driving motor at the low levelling speeds is effected by reversing the armature circuit of the main driving motor. It is therefore possible to obtain rapid and accurate levelling even though the ratio of running to levelling speed is very high.

Referring to the drawing, the motor 1 drives the generator 2 which supplies current to the car motor 3. When the car switch 4 is moved from the neutral position shown into engagement with up contact H2, it completes a circuit from the supply conductor 5 through the car switch, through the back contact d1 of the down contactor D through the winding of the up relay U and through the relay F to the other supply conductor 6. Contact. F1 of relay F completes the circuit of the field 2F of the generator. All of the resistance R is, at this time, in series with the generator field so that the voltage generated is low. The energization of the relay U has, in the meantime, simultaneously connected the motor 3 to the generator 2 through the contacts U3, Us in proper direction for upward movement of the car.

When the car switch 4 is brought into engagement with the contact H3 a circuit is completed from conductor 6 through the solenoid 9 and the car switch back to the other side of the line. The

solenoid or electromagnet 9 of an automatic levment of the car switch to the fourth position, in

engagement with contact H4, effects energization of the solenoid 1'? whose contact 18 there upon shunts out section r2 of the series field resistance R, for running of the car at second speed. When the voltage generated by the generator 2 has built up sufiiciently the relay 7 connected across the generator lifts its contact 8. Similarly, when the car switch 4 is moved to its final position in engagement with contact H5 the solenoid 19 is energized so that its contact 20 may shunt the section 13 of the field resistance provided that the potential relay 7 has closed contact 8. With all of resistance R shunted out,

the generator voltage applied to the motor is a maximum and the car runs up at high speed.

To stop the car at a desired landing, such as 21, the operator centers the car switch as he approaches the landing; i. e. he returns it to the neutral position shown in the drawing. As the contact 4 moves out of engagement with the contacts H5 and He, the section r2, 13 of the series field resistance is reinserted in circuit, reducing the output voltage of the generator to a low extent, whereupon the car speed drops to a suitably low value for accuratelevelling. As the contact 4 moves out of engagementwith the contact H3, the followers 12 and 13, under the influence of the biasing springs 22, 23, move into the path of the 20 levelling cam 16 for the selected floor. As the contact 4 moves out of engagement with contact H2 the fup" contactor U is deenergized and its contacts U3 and U4 fall to interrupt the armature circuit of motor 3. The relay F is also de- '95 energized so that contact Fl falls to open the generator field circuit. Simultaneously with opening of the motor circuit the back contact U2 -of the contactor U closes the dynamic braking circuit including the resistance B. A solenoid 30 i brake not shown is applied substantially simultaneously with rupture of the motor circuit.

Assuming that the car, in coasting to a stop, slightly over-travels, i. e. comes to rest slightly above the floor 21, the roller 13 of the automatic 2B5 levelling device, for that position of the car, is upon the high part of the cam 16, the overtravelling movement having efiected closure of the contacts V2, V3, the latter of which is carried by the arm 15. These contacts complete a. circuit HG through the back contact U1 of the up" relay U to the winding of the down contactor D, and the winding F of the field relay. Since the field of the generator hasnot been reversed, there is produced a low voltage of the same polarity, as ltd before. The energization of the down relay D through the relay contacts D3, D4, reconnects the motor 3 to the generator armature, but in reverse sense, so that the voltage applied to the motor armature is reversed and the car travels slowly 1% downward for relevelling. Since there has been no reversal of the generator held, the voltage applied to the motor for both the levelling up and levelling down is of the same magnitude. Moreover, the full levelling voltage, in reverse direc- 25 tion, is immediately applied, as distinguished from the prior arrangements in which, immediately upon reversal, the voltage even if of proper polarity was unduly low and built up slowly.

When the roller 13 rides off the high part of the 3133 cam, the circuit of the down contactor D and field relay F is broken by opening the contacts V2, V3. The deenergization of the field relay opens the field circuit, as before, and the voltage applied to the motor falls to zero. The deenergization of the down contactor D completes, through contact D2, the dynamic braking circuit including resistor B. The car, therefore, comes to rest -more or less exactly on level with the landing 21.

car is effected, while maintaining the field excitation in the same direction as before, by reversing the connections to the motor armature. The levelling operations, if more than one is necessary, occur in rapid sequence without substantial pause or hesitation, such as was inherent in the prior systems, because of their need for time to reverse and build up the generator field strength.

From the foregoing description, automatic ievelling operation for downward running of the car should be clear. To start the car down, the car switch t is swung in counterclockwise direction successively to engage the down contacts L2, L3, L4, L5. Briefly, engagement with contact L2 effects energisation of the generator field by actuation of relay F and connection of the motor 3 in proper direction for downward travel by the contacts D3, D4 of the down relay D; engag ment with the contact L3 effects movement of the rollers l2, 13 out of the paths of the levelling cams 16 so that a run of several floors can be efiected without interference by the automatic levelling; engagement with contacts D4, D5 efiects running of the car at third and fourth speeds, respectively. As before, the car is stopped by centering the car switch as it approaches the desired landing, whereupon the levelling cam 16 of that particular floor cooperates with the levelling switches V1, V2, W1, W2 to bring the car to a stop flush with the landing. The down and upward levelling is effected as before by the cooperation between the contactors D and U which control the reversal of the motor M by reversing its connections to the generator armature, the generator field remaining at the same polarity under all circumstances.

The directional relays are electrically interlocked by their back contacts D1. U1 so that both cannot be simultaneously energized to shortcircuit the generator armature.

While for purposes of explanation, I have illustrated and described a specific elevator control system, it is to be understood that my invention is not limited thereto but is co-extensive in scope with the appended claims.

What I claim is:

i. A high speed elevator system including a car motor and an individual generator connected to term a Ward-Leonard drive, control means operahie to reduce the field excitation of said generator to a value of the same order of magnitude as the residual field thereof for efiecting low speed levelv ling of the car, and means for selectively levelling the car in either direction at the same speed comprising means for reversing the armature conneotions between said motor and generator with out reversing said generator field.

2. A high speed elevator system including a car motor and an individual generator connected to form a Ward-Leonard drive, control means for reducing the speed of the car for levelling to such a value that the generator voltage due to the residual field is a substantial component of the total generator voltage, and means for reversing the car at said low speed without changing its speed comprising means for reversing the armature connections between said motor and generator and maintaining the same polarity of generator field.

3. A high speed elevator system including acar motor and an individual generator connected to form a Ward-Leonard drive, control means for reducing the speed of the car for levelling to such a value that the generator voltage is of the same order oi magnitude as the component of generator voltage due to the residual field, and means for automatically levelling the car in either direction at the same speed comprising means responsive to the car position for reversing only the armature connections between said motor and generator.

i, In ahigh speed elevator system including a car motor and an individual generator connected to form a Ward-Leonard drive and having an operating speed range including a given speed at which a substantial component of the generator voltage is due to its residual field, means for levelling the car at the same speed in either direction comprising means for reducing the speed of said car to said given speed and means for reversing only the armature connections between said motor and generator.

5. In a high speed elevator system including a car motor and an individual generator connected to form a Ward Leonard drive and having an operating speed range including a given speed at which a substantial component of the generator voltage is due to its residual field, means for automatically levelling said car in a levelling zone at the same speed in either direction comprising means for reducing the speed of said car to said given speed, and means responsive to the car posil tion for reversing only the armature connections between said motor and generator.

6. A high speed elevator system including a car motor and an individual generator connected to a Ward-Leonard drive, means for varying the speed of the car over a wide range comprising means for varying the field excitation of said generator over a range having a minimum value of the same order of magnitude as its residual field, and means for selectively operating the car in either direction at the same speed with said minimum generator field excitation comprising means for reversing only the armature connections between said motor and generator.

7. A high speed elevator system including a car motor and o 1 individual generator connected to form a V -Leonard drive, means for varying the speed of thecar over a wide range comprising a field resistance for said generator having a maximum setting corresponding to a field e citation of the same order of magnitude as the residual field of said generator, and means for selectively operating the car in either direction at the same speed with said maximum resistance setting comprising means for reversing only the armature connections between said motor and generator.

8. In a high speed elevator system including a car motor and an individual generator connected to form a Ward-Leonard drive and having an operating speed range corresponding to a range of generator field excitation including a given value of the same order of magnitude as the residual field thereof, the method of running the car at the same speed in either direction for said given field excitation which comprises reversing only the armature connections between said motor and generator.

9. In a high speed elevator system including a car motor and an individual generator connected to form a Ward-Leonard drive and having an operating speed range corresponding to a range of generator field excitation including a given value of the same order of magnitude as the residual thereof, the method of levelling the car at the same low speed in either direction comprising reducing the field excitation of said generator to said given value and reversing only the armature connections between said motor and generator. JOSEPH H. BORDEN. 

